1. Field of the Invention
The present invention relates generally to sealed sample pans, which are used with an autosampler mounted on a thermogravimetrical analyzer (TGA). More particularly, the present invention relates to sealed sample pans designed to keep the sample isolated from the ambient environment until the beginning of an experiment.
2. Background Information
A TGA is an instrument for measuring the thermal stability of a sample. The instrument heats a sample and measures the weight gain or loss during the process. In a typical instrument, a sample is suspended from a very sensitive balance. When heated, the sample undergoes a physical change. The weight versus temperature and weight versus time is then recorded and plotted for each sample. TGAs are described, for example, in U.S. Pat. No. 5,165,792, which is incorporated by reference herein.
A TGA autosampler is an accessory that is used to automatically load samples into and unload samples from a TGA. It allows a TGA to be operated unattended for long periods of time. It typically contains a programmable tray capable of holding between 16 and 64 sample pans and a mechanism for moving these pans between the tray and the TGA.
A sealed sample pan is the enclosure containing the sample to be tested. It is designed so that it can be moved automatically by the autosampler from the tray, to the TGA, and back to the tray. A sample is hermetically sealed in a sealed sample pan before it is placed on the autosampler tray. However, just before being placed in the TGA, each sample must be exposed to the ambient environment. As a result, the sealed sample pan must be opened just prior to loading it into a TGA.
The current known method of opening a sealed sample pan consists of piercing the pan with a tapered pin just prior to loading. This method has a number of disadvantages. One, because the piercing element penetrates the sample pan, it can easily touch the sample during or after the penetration and may contaminate it or may contaminate the next sample. Two, the size of the pierced hole is not repeatable due to variables in the system and may result in inconsistent test results. Three, there are no means to determine whether or not the pan was pierced during the process. This is important, because if the sample pan is not pierced, the results of the measurement would not be valid. Also, some sealed sample pans must be opened to expose the sample to oxygen so that it can oxidize. Other samples generate gases during heating and will explode if not opened.
In view of the foregoing, a substantial need exists for a sealed sample pan and systems and methods of opening a sealed sample pan just prior to loading that prevent sample contamination or cross contamination with other samples, produce an opening of repeatable size, and provide a means to determine whether or not the pan was opened during the process.